Variable stress ratio in cumulative fatigue damage: Experiments and comparison of three models

Abstract

Abstract

We use the results of new fatigue experiments conducted with variable load levels as well as variable stress ratios to critically assess three (two old and one relatively new) cumulative fatigue damage models. Such models are usually tested using multiple blocks of periodic loading with differing amplitudes. However, available data pertain to zero-mean loading, and do not investigate the role of the variable stress ratio (S _min/S _max). Here, we present experimental results for variable stress ratios. Two specimen geometries and two materials (Al 2014 and Al 2024) are tested. Manson's double linear damage rule (DLDR) gives the highest accuracy in predicting the experimental outcome, even in the presence of variable stress ratios, whereas predictions of the newer model (‘a constructive empirical theory for metal fatigue under block cyclic loading’, Proc. R. Soc. A, 2008, 464, 1161–1179) are slightly inferior. The widely used Miner's rule is least accurate in terms of prediction. The merits and drawbacks of these models, in light of the experimental results, are as follows. The DLDR, though accurate, has minor scientific inconsistencies and no clear generalization. The constructive model has possible generalizability and more appealing scientific consistency, but presently has poorer accuracy. Miner's rule, though least accurate, lies within the constructive approach for special parameter values. The DLDR can guide the new (constructive) approach through new parameter fitting criteria.